More than half the global population now pay to use a mobile phone, according to a new UN report. With this breathtaking surge in users has come a huge expansion in the mobile services available, from instant money transfers to public health advice to internet access. The fastest growth has been in Africa where people like Deograsias Mukeba, from the Democratic Republic of Congo, now find their phones indispensable.

For much of his life, Mukeba didn't have an address. His corrugated iron house had no number and his volcanic ash street in the heart of Goma had no name. There was no postal service and the phone system had long since disintegrated. So when his mother died in 1995 on the other side of the Democratic Republic of Congo, her church sent a note marked only "Deograsias Mukeba, Goma". Remarkably it got to him - but three weeks after the funeral.

That was before. Now Mukeba's address goes with him everywhere. It has transformed the 33-year-old's life. It is an old Nokia mobile phone. "It was very hard discovering my mother had died and been buried and I didn't know anything about it for weeks," said Mukeba. "But that's how life was. If you lived in Goma, Kinshasa was another planet.

"I didn't really have any work. When the cell phones came I found the money and bought one because it was cool to have. It cost me $25 (£18). It's a lot.

"My brother lives in Kinshasa where he is a trader. He called me and asked me to start finding some things for him that you couldn't get in Kinshasa but you could find in Rwanda and Uganda, like some electrics and car parts. Now I speak to him every day. I send a lot of stuff. Now we are making money."

Mobile phones have changed Congo irrevocably, especially Goma. The country has only about 20,000 land lines after the system collapsed under Mobutu Sese Seko's ruinous dictatorship.

Now traders shipping imports to distant towns, farmers sending produce to the main cities, and those involved in the thriving gold and diamond smuggling trade use their phones to check prices, text quotes and arrange deliveries. Women who once sold roasted corn by the roadside now make a living dealing in mobile top-up cards and recharging flat phone batteries in a town where much of the population doesn't have electricity.

"Everyone but the very poor has a cell phone," said Mukeba. "Even the guy who only makes a few dollars a day picking up passengers on his bike. Even the woman selling things by the roadside. Almost everyone finds the money."

Cell phones have helped transform Goma in other ways. The town's economic boom of recent years has been fuelled by war and plunder, particularly of the rich mines in eastern Congo. Among them are diamonds and gold but also coltan, a rare but crucial element in mobile phones.

The small fortunes to be made by mining it sent tens of thousands digging for black mud and attracted criminal syndicates and foreign armies. "It all came at once," said Mukeba. "War, cell phones, dollars. Some people are getting very, very rich and everyone is making a little bit of money."